For cosmetics, in order to impart smoothness and a moist feeling to the skin and hair, oily agents, e.g., hydrocarbon oils such as liquid paraffin and squalane, oils and fats and triglycerides represented by vegetable oils, ester oils having an ester linkage, silicone oils such as dimethylsiloxane, and the like are employed. In particular, oily agents that are transparent liquids and have a low viscosity at ordinary temperature have been frequently used owing to a good feeling.
Examples of transparent cosmetics highly blended with an oily agent may include cleansing oils, hair oils, massage oils, and the like. An excellent structure-recovering property may be mentioned as a consumer's need for these cosmetics in recent years.
The structure-recovering property is a property that viscosity decreases by the action of an external force but returns to the original one when the external force is suppressed. In general, a low-viscosity oily agent causes liquid dripping when taken in the hand, and thus it is difficult to apply it to a suitable part of the skin in a proper quantity. Therefore, it is required to have a high viscosity at the time when it is taken out of a vessel or before it is applied to the skin. On the other hand, at the time when it is applied (an external force is imparted), it is required not to impair the smoothness intrinsic to the oily agent. That is, when a feeling in use is good and the structure-recovering property is exhibited, added value of commercial products can be enhanced.
In order to impart the structure-recovering property, it is common to add a gelling agent or thickening agent (hereinafter referred to as gelling agent) to control the viscosity, but it is technically difficult to obtain a transparent gel in an oily system. As the reasons, there are mentioned the fact that the oily agent includes various chemical substances such as hydrocarbon oils, vegetable oils and triglycerides, ester oils, and silicone oils and thus there are many kinds of media and the fact that it is difficult to form an association by the action of electric charge since electric conductivity is poor unlike the case in an aqueous system. Therefore, in order to control viscosity in an oily system, it is common to utilize aggregation induced by a gelling agent or a crystal structure, so that it is difficult to obtain a transparent cosmetic composition and there has not been obtained a cosmetic composition which satisfies a feeling in use at the time when it is applied to the skin or hair.
Namely, it has been desired to develop a cosmetic composition which has the structure-recovering property, is transparent, and exhibits a good feeling in use, with containing a large amount of an oily agent.
In order to enhance the viscosity of the oily agent, some gelling agents have been hitherto proposed and oily gelling agents having a hydrogen bond part such as a hydroxyl group or an amide group have been developed. For example, a technology using 12-hydroxystearic acid and a dextrin fatty acid such as dextrin palmitate (Patent Document 1), an N-acylamino acid derivative such as N-2-ethylhexanoyl-L-glutamic acid dibutylamide (Patent Document 2), and the like have been proposed. They have a thickening mechanism dependent on a hydrogen bond which strongly interacts even in an oil and exhibit a gelling effect in a small amount, but they are not suitable for use in preparations which particularly require the structure-recovering property.
Moreover, a gel composition containing a specific polyoxyalkylene ether that is a block-type alkylene oxide derivative and an oily agent and water has been also proposed (Patent Document 3). The composition has a gel-forming ability having an excellent structure-recovering property (thixotropic property) and a transparent feeling, but there is a further room for improvement in a feeling in use, for example, a feeling when applied and spreadability.